•Gold and Silver medals of the Exhibition of Economic Achievements of the USSR (Domesticated foxes)•Prize of the Presidium of the Academy of Sciences of the USSR named acad. N.I. Vavilov (1985)•The Order of the Badge of Honor (August 21, 1986)•Winner of 2018 The American Association for the Advancement of Science (AAAS)/Subaru Science Books & Film Prizes for Excellence in Science Books

In 1952 Dmitry Belyayev started an experiment to try to create domesticated foxes from relatively wild foxes that had been in captivity. He chose to work with the Silver Fox, a variant of the Red fox,Vulpes vulpes. The experiment was moved to Novosibirsk, Russia, in 1959 at the Institute of Cytology and Genetics with 30 males and 100 females. Lyudmila Trut was chosen as manager of the program. Trut and Belyayev applied one selection criterion, and that was to select for "tameness." Each generation of foxes was scored for "tameness", which started when a fox pup was about one month old. Experimenters offered food from their hand while trying to stroke and handle the pup; at sexual maturity, at seven or eight months, the pups were scored and placed in three classes ranging from less tame to most tame. By the sixth generation an additional class was created for the "domesticated elite." These were foxes that were eager to have human contact. By the 10th generation 18 percent of fox pups were in this "elite" class; by the 20th generation 35% were "elite", and by the 30th generation 70% to 80% of the selected generation was "elite."[4]

In 1978 Belyaev reported at an Invitational Lecture at the 14th International Congress of Genetics in Moscow the types of changes that were observed by Belyaeva and Trut in the tame-selected foxes.[5] As early as the second generation, counting from 1959, the "tameness" score of the selected population continued to increase every generation. "Tail wagging" was observed in one male fox by the fourth generation (1963).[3] As early as 1962 changes in the animals reproductive behavior started taking place. They found that some of the "tame" foxes were showing signs of "proestrus", as early as October–November, as opposed to the normal time of January–March. By 1972 some females were coming into estrus in the October–November period. However, the males were not ready for mating. By 1976 the tamest females mated as early as December 20; some of the females gave birth and then mated again in March–April.[5] In the 10th generation (1969), "floppy ears" appeared in a female pup, as well as a piebald coloration on other tame pups consisting of patches of white and brown on the belly, tail, and paws. A small white "star patch" appeared in the middle of forehead of one pup also in the 10th generation.[3] Other correlated changes in the domesticated foxes reported by Belyaev[5] included a shortened tail, a shortening and widening of the skull, and the tail rolled over the back.

L. Trut and domestic Fox-1974

Detailed genetic and physiological studies on these foxes have been done by Trut and colleagues. For example, the "star-shaped" pattern was found to be controlled by one dominant gene that was incompletely penetrant, "but its penetrance is significantly higher in offspring from tame mothers than from aggressive ones..."[6] Trut reported that female foxes heterozygous for the gene controlling the star pattern also influenced the number of male pups, increasing the number of males over the expected 50%. Further, as the fox experiment has progressed over time, it was found that in general the number of male pups increased over the expected 50% to approximately 54%.[7] Early in the experiment Trut and Belyaev started comparing the hormonal responses of the tame and control foxes.[5][8] They showed that selection for tame behavior caused the levels of 11-oxycorticosteroids in the blood to be reduced; selection had also caused the morphology of adrenal glands to change. Levels of the sex hormones estradiol and progesterone differed. Belyaev[5] stated: "Perhaps the most important observation emerging from this series of experiments is that fact that tame females exhibit statistically significant changes in certain neurochemical characteristics in such regions of the brain as the hypothalamus, midbrain, and hippocampus. The level of serotonin and its metabolite 5-hydroxyindoleacetic acid turned out to be higher in tame than in unselected females. This fact fits the type of behavior, since serotonin is known to inhibit some kinds of aggression. Moreover, serotonin plays a role in the central regulation of the hypothalmic-hypophyseal-adrenal-sexual system. Thus, selection for tame behavior is associated with changes in both the central and peripheral mechanisms of the neuro-endocrine control of ontogeny."

Trut and her colleagues have applied modern molecular techniques to the fox populations with the aim of not only identifying which genes are involved in domestication, but also in determining how changes in the fox genome compare to those of the domesticated dog.[9][10][11][12] 400 canine microsatellites that are evenly distributed across the canine genome were analyzed in the fox genome. Based on amounts of homozygosity in both tame and aggressive foxes, it was found that there was no evidence of inbreeding between the two groups of foxes. Further, to help understand the neurobiology of behavior, fox and dog orthologs of serotonin receptor genes were cloned.[9] Using 320 microsatellites Trut and co-workers showed that all 16 fox autosomes and one X chromosome were covered, and that there was a high conservation of marker order between homologous regions of foxes and dogs, even though the fox genome has 16 pairs of metacentricautosomes and the dog has 37 pairs of acrocentricautosomes.[10] Additional studies by these workers has shown that "tameness" and "aggressiveness" is associated with at least two loci.[12]